An exhaust system comprises, in the usual manner, an exhaust line, which has at least one exhaust pipe, whose pipe wall defines with an inner side an exhaust gas path for guiding an exhaust gas flow. The exhaust line begins at the engine block of the internal combustion engine, as a rule, with an exhaust manifold or exhaust collector and ends towards the surrounding area with at least one tail pipe. A plurality of exhaust gas treatment devices, for example, catalytic converters and particle filters, are integrated into the exhaust line. Further, the exhaust line usually contains at least one muffler. To connect the individual components with one another, the exhaust line contains aforementioned exhaust pipes. Sensors for measuring parameters of the exhaust gas flow and/or of the exhaust system as well as injectors for introducing a reactant, especially a reducing agent or an oxidizing agent, or the like into the exhaust gas flow may be arranged in the area of these exhaust pipes on the exhaust line.
Different temperatures prevail within the exhaust system from the exhaust manifold to the tail pipe during the operation of the exhaust system. There is a risk of condensation and the formation of deposits in the interior of the exhaust line in colder areas. For example, a film of combustion residues, for example, soot, water or hydrocarbons, may become deposited on the inner side of the pipe wall. If an aqueous urea solution is introduced as a reducing agent into the exhaust gas flow, for example, in connection with an SCR system, in which SCR denotes Selective Catalytic Reduction, there is, in addition, a risk that urea crystals will form. These contaminants within the exhaust line may compromise, for example, the guiding of the exhaust gas flow. Further, these contaminants may represent an increased risk of corrosion for the affected pipe wall. The risk of such condensation and deposit formation is especially great particularly in case of a cold start as well as when driving over short distances, because the pipe walls affected are still at a comparatively low temperature level, on the one hand, and since relatively high temperatures are needed to remove the deposits, on the other hand.
To counteract these problems, it is possible, in principle, to heat the exhaust gas flow more intensely, as a result of which the exhaust line as a whole can be brought to an elevated temperature level more rapidly. Electrically heatable catalytic converters, which are usually called EKAT, may be used here. However, such an EKAT requires a comparatively large amount of energy to be able to heat the relatively large exhaust gas mass flow correspondingly. An additional problem arises here concerning the electrical insulation of the high electric currents against the metallic components of the exhaust line when corresponding electric lines must be passed through a usually metallic pipe wall.